1. Field of the Invention
The present invention relates to an image pickup apparatus, and more particularly to an image pickup apparatus characterized by its zoom mechanism.
2. Description of the Related Art
Conventionally, there have been proposed various techniques concerning a zoom lens barrel which is extended from the body of an image pickup apparatus for shooting and retracted into the apparatus body for accommodation. This type of zoom lens barrel is formed by combining a plurality of rectilinear motion barrels and rotary barrels, and is configured to be advanced and retracted along an optical axis direction.
By combining a plurality of barrels, it is possible to form a lens barrel having a long total length. Further, it is possible to accommodate these barrels in the apparatus body when not in use to thereby reduce the thickness of the image pickup apparatus.
There has been proposed in Japanese Patent Laid-Open Publication No. 2000-111786 a multi-stage lens barrel mechanism comprised of a plurality of intermediate barrels each formed by combining a single rotary barrel and a single rectilinear motion barrel.
In the lens barrel mechanism disclosed in Japanese Patent Laid-Open Publication No. 2000-111786, the multi-stage structure thereof is formed by arranging a plurality of parts each formed by combining a single rotary barrel and a single rectilinear motion barrel. In this construction, the rotational force of each rotary barrel is obtained by converting the motion of the barrel along the optical axis direction into rotation by a cam.
For example, in a U-turn optical system wherein a lens is temporarily moved toward an image forming side in a process of zooming from the wide-angle end to the telephoto end, the direction of travel of the rotary barrel along the optical axis is changed during the zooming, and hence there is a moment when the amount of motion of the barrel becomes zero.
At this moment, in the lens barrel mechanism, where the motion of the barrel along the optical axis is converted into rotation by the cam, no rotational force is generated in each intermediate barrel.
Further, in a conventional lens barrel mechanism using helicoids, when a multi-stage restract mechanism is employed that is formed by combining helicoids arranged in the direction of extension of the lens barrel in a uniformly angled state, it is difficult to change the direction of travel of the intermediate barrels along the optical axis during zooming.